It sounds like you already have your mind made up to go with Hans.
I've had Stendkers (not directly from Hans but from a store he supplied) and I've had Asian fish from two separate importers (Kenny and Mike Beals). Tank-bred discus are tank-bred discus. They're all fine in most tap water as long as you don't have really weird parameters like high nitrates or something. Care is the same for any discus you get, regardless of its origin. The real difference comes down to what you want in a discus. European bred discus tend to come in more traditional strains and are usually large-growing, while Asian fish tend to come in more trendy colors and don't always grow as large (though this is just speaking in general terms; I've definitely seen giant Asian discus).
I would recommend sticking with one supplier for your first purchase. It's best to buy all your new discus at once. If you go with Hans, order everything from Hans.
You can mix Asian and German discus but not without following strict quarantine procedures. Always quarantine everything. It doesn't matter where it comes from. If you already have a tank full of Asian discus and you buy more Asian discus, the new ones should still be quarantined. Same for German fish. Same for wild fish. Any fish can be a carrier for any disease at any time. Your new fish could pass on things to your existing stock, or your existing stock could infect new fish with something they have.
Read these threads:
http://forum.simplydiscus.com/showth...tendker-Discus
http://forum.simplydiscus.com/showth...Kenny-s-Discus